1. Field of the Invention
The present invention generally relates to remote measurement and telemetry and, more particularly, to rapid and automated measurement of material levels in containers or vessels and reporting of the results thereof.
2. Description of the Prior Art
Commercial and industrial environments present numerous circumstances and environments in which rapid measurement and reporting of material levels is required. Many require continuous or rapidly repeated (e.g. several times per second or more to support analysis of level variance) monitoring and/or measurement of many levels of many different materials in many containers substantially simultaneously.
While many sensors for measurement of material level are known, many are restricted to particular materials or materials having particular properties such as float sensors or optical reflection sensors for liquids while such sensors are inapplicable to solids. For example, a float of a float sensor may be buried by granular solid materials or fouled by viscous or adhesive materials while granular materials will not make intimate contact with the detection surface of an optical liquid level sensor which viscous or adhesive materials may also foul. Mechanical and optical sensors also tend to be expensive and generally introduce non-linearities (e.g. by a pivoting mechanism or discrete optical surfaces) into the measurement. Further, while these devices may provide effective measurement, they do not generally provide communication of the measurement results and complex additional wired and/or wireless communication systems must be employed in order to do so; often of substantial geographical extent. Such communication systems and hardware elements thereof as well as level sensors may have substantial sensitivity to the measured material which may, for example, present conductive, explosive or corrosive environments or otherwise constitute a potential source of damage to the communication system or present a potential safety hazard.
Moreover, level sensor systems can be quite expensive, especially when a large number of such sensors are required. Additionally, different types of level sensors adapted for different materials may produce outputs in a wide variety of forms and are not inherently calibrated, particularly among the different known types of level sensors. Therefore, substantial processing of the sensor outputs is generally required when material level sensors of different types are employed in a single system.
Radio frequency identification (RFID) systems are also known, principally for article placement and removal detection systems and systems intended to deter theft. In most such systems in current use, a transponder, often referred to as a tag (or RFID tag), is attached to an article of interest and produces a detectable radio frequency signal when interrogated. RFID tags may be either active (e.g. having a power supply associated therewith) or passive (e.g. deriving power from the interrogation signal to charge a capacitor) and may be extremely simple and inexpensive to produce. Perhaps the simplest form of an RFID tag involves an antenna and a very few circuit elements which receive a radio frequency (RF) signal of one frequency which is converted to another frequency and re-radiated. The necessary circuit elements and antenna of the RFID tags can be inexpensively produced together as a single unit in very large numbers by simple printing and laminating processes.
Such tags are often employed for theft deterrence where many articles must be protected by placing a transmitter/receiver unit near a point of egress from the protected premises. If a tag attached to a protected article is brought within range of such a detection unit, the tag will receive a signal, effectively interrogating the transponder, and the returned signal will be detected and the movement of the object reported by an alarm or the like. With only a small increase in complexity and cost, a substantial number of transponders of either the active or passive type can be made uniquely identifiable such as by providing detectably different frequencies as the return frequency. Transponders may also be uniquely identified by providing unique codes to be returned such as for use in automatic toll collection. However, at the present state of the art, the principal application of RFID systems has generally exploited the ability to use inexpensive tags to monitor large numbers of objects at particular locations rather for identification of individual objects.
Further, since transponder tags must be attached to or otherwise integrated with the monitored objects, RFID systems have not been useable for loose solid materials or liquids. In other words, known RFID systems may be readily applied to containers of liquids and packages of materials such as sacks of grain, sand, concrete and the like but not to the material itself such as when a fungible material (e.g. metal scrap, sand, concrete, etc.) is placed in or removed from a container.